Standby power consumption reduction is becoming a major issue for appliances and devices, supplied from the utility grid, such as consumer lifestyle appliances or networked lighting ballasts. In the past, solutions have been proposed, which solved the above problem by using a very-low-power controller circuit in combination with an energy storage element and a bi-stable or latching relay. Major disadvantages of the relay are the audible switching noise, the limited lifetime, the large physical size, limited reliability under mechanical shocks, and eventually high cost. Audible noise and mechanical wear during switching mandates avoiding frequent recharging of the energy storage and thus demands for a substantial capacity of the storage element, leading to higher cost. Return of the mains voltage after a blackout leads to synchronous inrush current of all connected devices which may trip circuit breakers and thus may lead to another blackout.
A simple replacement of the mechanical relay by a semiconductor switch has the disadvantages of risking dead-lock situations after mains blackout and depletion of the energy storage element in consequence. There is also a constant effort keeping it into a desired state, compared to the latching or bi-stable relay solution.